Thank you for the suggestion. Hopefully I have found my problem.
Yesterday I using my computer without a web page being loaded. All of a sudden Firefox started and displayed a William Hill gambing page. This made me thing that I must have a virus / adware running.
Since Windows 8 came out I have been relying on Windows Defender for security, and this has not notified me of any problems. So I decided to revert back to AVG Free. This found and removed
AdInstaller Astromenda and
InstallCore in c:\users... I can't be sure where these came from but I did find that a few files that I have downloaded in the past where infected. Including a copy of Imgburn version 2.5.8.0
I am tempted to suggest that Microsoft should put more effort into developing Windows Defender rather than Windows 10. I am a little surprised that companies such as Ladbrokes and William Hill should rely on such dubious processes for promoting their products.
Michael Chare